1. Field of the Invention
The present invention relates to an optical disk device, and more particularly to optimization of power level for recording data on a writable optical disk.
2. Description of the Related Art
Optimum Power Control (OPC) is a known technique to optimize recording power level by recording test data on a predetermined area (PCA area) of a writable optical disk, reproducing the data, and evaluating reproduced signal quality.
Nevertheless, due to temperature change within an optical disk drive or quality variance of a laser diode (LD), a recording power level yielding the optimum value of reproduced signal quality may exceed the maximum allowable power level of the laser diode. In such a case, recording cannot be performed at the actual optimum recording power level. Recording must instead be carried out at the maximum allowable power level of the LD, which is lower than the optimum power level.
Japanese Patent Laid-Open Publication No. Hei 9-288827, for example, discloses maintaining recording quality by adjusting the rotational frequency of an optical disk during data recording, when, upon conducting OPC, the optimum recording power level exceeds the maximum allowable power level of the LD. Specifically, when the optimum recording power level determined by OPC exceeds the maximum allowable power level of the LD, the rotational frequency is adjusted so as to be lower according to:f′=f·(Plim/Po)2Here, f′ is the rotational frequency after the adjustment, f is the normal rotational frequency before the adjustment, Plim is the maximum allowable power level, and Po is the optimum power level. By reducing the rotational frequency in this manner, data can be recorded at the optimum power level lowered to match the maximum allowable power level.
However, it is generally difficult to control the rotational frequency with high accuracy. Moreover, reduction of rotational frequency leads to decrease in recording speed, making it difficult to fulfill the demands for high-speed recording.
Japanese Patent Laid-Open Publication No. 2001-143263 describes a technique in which, when the recording pulse comprises a leading pulse and a subsequent pulse array, OPC is performed while simultaneously varying duty and recording power conditions for the leading pulse and the subsequent pulse array, so as to search for the recording condition yielding minimum jitter. This technique is disadvantageous in that the OPC processing is complex, basically requiring test recordings to be performed for the number of possible combinations of three parameters.